After a stainless member is processed into a predetermined shape by forging or rolling, the forged stainless member or the like may be subjected to solutionizing heat treatment.
For example, PTL 1 discloses technology in which a stainless member forged at a high temperature of 1000° C. to 1300° C. is cooled, and then is subjected to heat treatment at a high temperature of 950° C. to 1125° C. again. In this technology, the heated stainless member is quenched at a cooling speed of 4° C./min to 5° C./min.
PTL 2 discloses technology other than the technology disclosed in PTL 1, which is related to the present invention. In this technology, after an aluminum alloy member is heated for heat treatment, the aluminum alloy member is quenched by blowing a cooling medium to the aluminum alloy member via multiple nozzles. In a case where a metal member is quenched, a high-temperature portion, the temperature of which is easily decreased, and a low-temperature portion, the temperature of which is not easily decreased, are formed in the metal member depending on the shape of the member. As a result, thermal stress and strain occur in the metal member during a cooling process of the metal member. In the technology disclosed in PTL 2, the flow rate of the cooling medium blowing via the multiple nozzles is adjusted to suppress the occurrence of strain in the quenching process of the aluminum alloy member.